The S4 segment comprises part of the voltage sensor in Shaker K+ channels. We have used a strategy similar to intragenic suppression, but without a genetic selection, to identify electrostatic interactions of the S4 segment that may be important in the mechanism of voltage-dependent activation. The S4 neutralization mutations K374Q and R377Q block maturation of the protein, suggesting that they prevent proper folding. K374Q is specifically and efficiently rescued by the second site mutations E293Q and D316N, located in putative transmembrane segments S2 and S3, respectively. These results suggest that K374, E293, and D316 form a network of strong, local, electrostatic interactions that stabilize the structure of the channel. Some other double mutant combinations result in inefficient suppression, identifying weak, presumably long-range electrostatic interactions. A simple structural hypothesis is proposed to account for the effects of the rescued double mutant combinations on the relative stabilities of open and closed channel conformations.

Delineating neurons that underlie complex behaviors is of fundamental interest. Using adenoassociated virus 2, we expressed the Drosophila allatostatin receptor in somatostatin (Sst)-expressing neurons in the preBötzinger Complex (preBötC). Rapid silencing of these neurons in awake rats induced a persistent apnea without any respiratory movements to rescue their breathing. We hypothesize that breathing requires preBötC Sst neurons and that their sudden depression can lead to serious, even fatal, respiratory failure.The preBötC in the ventrolateral medulla is hypothesized to be a kernel for the generation of respiratory rhythm in vitro and in vivo 1-4 . Adult rats with slow (~days), toxin-induced neurodegeneration of > 80% of neurokinin 1 receptor (NK1R)-expressing preBötC neurons survive with an ataxic rhythm during wakefulness and apnea during sleep 1,5 . Whether this pathological breathing pattern is driven by neurons that normally control respiratory-related muscles, including those underlying volitional or emotional behaviors, or by a compensatory reorganization in response to the slow neurodegeneration is unknown. To eliminate adaptation resulting from slow lesions, we rapidly (~minutes) decreased excitability in a glutamatergic subpopulation of preBötC neurons that express Sst 6 . This population overlaps with neurons expressing NK1R; 28 ± 2% of preBötC Sst neurons expressed NK1R and 41 ± 1% of preBötC NK1R neurons expressed Sst (5-6-week-old rats, n = 3; Supplementary Fig. 1 online), consistent with their overlap in neonatal rat preBötC 7 . We hypothesized that preBötC Sst neurons are essential for normal breathing and predicted that silencing these neurons would cause acute apnea in awake adult rats; as hypoxia and hypercapnea worsened with apnea, we presumed that other mechanisms, particularly in relation to volitional or emotional drives, would restore breathing, as appears to be the case in central congenital hypoventilation syndrome 8 . Rapid, reversible silencing of genotypic neuronal subpopulations can illuminate their role in behavior. This can be done by targeted expression of allatostatin receptor (AlstR), a G protein-coupled receptor that is neither expressed nor activated by any endogenous ligand in mammals 9-11 . Mammalian cortical and spinal cord neurons that are made to express AlstR can be rapidly and reversibly inactivated in vitro 12,13 and in vivo under anesthesia 10 by administration of allatostatin, which opens K + channels 9,13 to hyperpolarize them. WeCorrespondence should be addressed to J.L.F. (feldman@ucla.edu). 3 These authors contributed equally to this work.Note: Supplementary information is available on the Nature Neuroscience website. expressed AlstR and enhanced green fluorescent protein (EGFP) in targeted preBötC neurons and studied the effect of allatostatin application on breathing in adult rats. NIH Public AccessTo obtain stable and reliable expression of exogenous genes in adult rat preBötC neurons, we used adeno-associated virus 2 (AAV2) to ensure high infecti...

Breathing pattern is postulated to be generated by brainstem neurons. However, determination of the underlying cellular mechanisms, and in particular the synaptic interactions between respiratory neurons, has been difficult. Here we used dual recordings from two distinct populations of brainstem respiratory neurons, hypoglossal (XII) motoneurons, and rhythmogenic (type-1) neurons in the preBötzinger complex (preBötC), the hypothesized site for respiratory rhythm generation, to determine whether electrical and chemical transmission is present. Using an in vitro brainstem slice preparation from newborn mice, we found that intracellularly recorded pairs of XII motoneurons and pairs of preBötC inspiratory type-1 neurons showed bidirectional electrical coupling. Coupling strength was low (<0.10), and the current that passed between two neurons was heavily filtered (corner frequency, <10 Hz). Dual recordings also demonstrated unidirectional excitatory chemical transmission (EPSPs of approximately 3 mV) between type-1 neurons. These data indicate that respiratory motor output from the brainstem involves gap junction-mediated current transfer between motoneurons. Furthermore, bidirectional electrical coupling and unidirectional excitatory chemical transmission are present between type-1 neurons in the preBötC and may be important for generation or modulation of breathing rhythm.

A key distinction between neural pacemaker and conventional network models for the generation of breathing rhythm in mammals is whether phasic reciprocal inhibitory interactions between inspiratory and expiratory neurons are required. In medullary slices from neonatal rats generating respiratory-related rhythm, we measured the phasic inhibitory inputs to expiratory neurons with the use of whole cell patch clamp in the hypothesized rhythm generation site, the pre-Bötzinger complex (pre-BötC). Expiratory neurons, which generate tonic impulse activity during the expiratory period, exhibited inhibitory postsynaptic potentials (IPSPs) synchronized to the periodic inspiratory bursts of the hypoglossal nerve root (XIIn). Bath application of the glycine receptor antagonist strychnine (STR; 5-10 microM) reversibly blocked these inspiratory-phase IPSPs, whereas the gamma-aminobutyric acid-A (GABA(A)) receptor antagonist bicuculline (BIC; 10-100 microM) had no effect on these IPSPs. Replacing the control in vitro bathing solution with a Cl(-)-free solution also abolished these IPSPs. Respiratory-related rhythmic activity was not abolished when inspiratory-phase IPSPs were blocked. The frequency and strength of XIIn rhythmic activity increased and seizurelike activity was produced when either STR, BIC, or Cl(-)-free solution was applied. Inspiratory-phase IPSPs were stable after establishment of whole cell patch conditions (patch pipettes contained 7 mM Cl-). Under voltage clamp, the reversal potential of inspiratory-phase inhibitory postsynaptic currents (IPSCs) was -75 mV. The current-voltage (I-V) curve for IPSCs shifted to the right when extracellular Cl- concentration was reduced by 50% (70 mM) and the reversal potential was reduced to -60 mV, close to the new Cl- Nernst potential. In tetrodotoxin (0.5 microM) under voltage clamp (holding potential = -45 mV), local application of glycine (1 mM) over pre-BötC induced an outward current and an increase in membrane conductance in expiratory neurons. The effect was blocked by bath application of STR (0.8-1 microM). Local application of the GABA(A) receptor agonist 4,5,6,7-tetrahydroisoxazolo[5,4-c]pyridin-3-ol (THIP, 1 mM) induced an outward current and an increase in membrane conductance that was blocked by BIC (10-100 mM). Under voltage clamp (holding potential = -45 mV), we analyzed spontaneous IPSCs during expiration in expiratory neurons. Bath application of BIC (10 microM) reduced the IPSC frequency (from 2.2 to 0.3 per s), whereas the inspiratory-phase IPSCs did not change. Bath application of STR (8-10 microM) abolished both IPSCs. These results indicate that 1) reciprocal inhibition of expiratory neurons is glycinergic and mediated by a glycine-activated Cl- channel that is not required for respiratory-related rhythm generation in neonatal rat medullary slices; 2) endogenous GABA and glycine modulate the excitability of respiratory neurons and affect respiratory pattern in the slice preparation; 3) both glycine and GABA(A) receptors are found on pre-BötC expiratory...

Alcohol use disorders (AUD) constitute the most common form of substance abuse. The development of AUD involves repeated alcohol use leading to tolerance, alcohol withdrawal syndrome (AWS), physical and psychological dependence, with loss of ability to control excessive drinking. Currently there is no effective therapeutic agent for AUD without major side-effects. Dihydromyricetin (DHM, 1 mg/kg, i.p. injection), a flavonoid component of herbal medicines, counteracted acute alcohol (EtOH) intoxication, and also withdrawal signs in rats including tolerance, increased anxiety and seizure susceptibility; DHM greatly reduced EtOH consumption in an intermittent voluntary EtOH intake paradigm in rats. GABAA receptors (GABAARs) are major targets of acute and chronic EtOH actions on the brain. At the cellular levels, DHM (1 μM) antagonized both acute EtOH-induced potentiation of GABAARs and EtOH exposure/withdrawal-induced GABAAR plasticity, including alterations in responsiveness of extra- and post-synaptic GABAARs to acute EtOH, and most importantly, increases in GABAAR α4 subunit expression in hippocampus and cultured neurons. DHM anti-alcohol effects on both behavior and CNS neurons were antagonized by flumazenil (10 mg/kg in vivo, 10 μM in vitro), the benzodiazepine (BZ) antagonist. DHM competitively inhibited BZ-site [3H]flunitrazepam binding (IC50, 4.36 μM), suggesting DHM interaction with EtOH involves the BZ-sites on GABAARs. In summary, we determined DHM anti-alcoholic effects on animal models, and determined a major molecular target and cellular mechanism of DHM for counteracting alcohol intoxication and dependence. We demonstrated pharmacological properties of DHM consistent with those expected to underlie successful medical treatment of AUD; therefore DHM is a therapeutic candidate.